This invention relates generally to subsurface well apparatus and more specifically, to methods and apparatus for perforating subsurface earth formations utilizing a tubing conveyted perforating apparatus.
It has become common practice in completion of oil and gas wells to perforate the well casings and the surrounding formations to bring a well into production. One method of providing this capability has a perforating apparatus attached to the end of a tubing string which is lowered and set in place when the perforating apparatus is opposite the formation to be produced. The perforating apparatus may then be detonated and the well placed into production throught the tubing strings. It has also become common practice in the completion of oil and gas wells using the tubing conveyed perforating methods to intentionally create a pressure differential between the formation and the well bore to remove well bore fluids and debris immediately prior to and during the perforating procedure. This removal of fluids and debris is done to prevent clogging of the perforations, thereby increasing the efficiency of production. One method of providing this capability is to use a venting system which allows the fluids and debris to enter the tubing annulus to be removed at the surface.
The venting systems have typically been either an open perforated nipple or a mechanically actuated device Neither system is entirely satisfactory because open perforated nipples cannot be used when the well bore fluids are under pressure, and the mechanically actuated devices utilize moving parts which may become damaged when placed in the well bore or may stick and never open.
These and other disadvantages are overcome with the present invention by providing an explosively actuated venting system which can be used in high pressure well bores and has no moving parts to fail or stick.